2). Needs triggering, a little more complicated.
(My suggestion, passive mana burn ability "feedback" from arcane towers with a trigger detecting an attack against an enemy with mana draining mana from the attacking unit)

basic idea was make a global region and when a unit gains a buff have it be uncontrollable and get it to run to a random point in the region wait a second and have it run agian. when the buff leaves the tigger deactivates